1. Field of the Invention
The present invention relates to a voltage regulating system that is used in a car and used to regulate the output voltage of a generator, while the generator operates at low speed.
2. Description of Related Art
In general, the generator that is used in a car outputs a voltage according to the operation speed of the car engine. The output voltage of the generator charges a battery and provides power to all electronic devices of the car. Moreover, for petrol cars, the output voltage of the generator provides the current required to run the car engine.
The car usually has a voltage regulator to regulate the output voltage of the generator so as to avoid unstable output voltage. The voltage regulator regulates the output voltage down, while the output voltage is too high, and regulates the output voltage up, while the output voltage is too low. Therefore, the voltage regulator can stabilize the output voltage of the generator so as to provide stable power to every electronic device of the car and to prevent damage of the electronic devices.
FIG. 1 is a circuit diagram of a prior art voltage regulating system. As shown in FIG. 1, a voltage regulator 10 of the voltage regulating system 1 has three terminals A, F and G, wherein terminal A of the voltage regulator 10 connects to the first output terminal T1 of a generator 12, and connects to the second output terminal T2 of the generator 12 via a warning light 14 and a starting switch 15. Moreover, terminals A and F of the voltage regulator 10 connect to an exciting winding 122 of the generator 12, and terminal G of the voltage regulator 10 connects to ground g. The voltage regulating system 1 further includes a battery 13, wherein the positive terminal of the battery 13 connects to the second output terminal T2 of generator 12, and the negative terminal of the battery 13 connects to ground g.
Please refer to FIG. 1 again. The voltage regulator 10 includes a current limit resistor Rb, wherein one terminal of the current limit resistor Rb connects to terminal A of the voltage regulator 10, and another terminal of the current limit resistor Rb connects to the base of a Darlington transistor Q. The collector of the Darlington transistor Q connects to terminal F of the voltage regulator 10 and connects to terminal A of voltage regulator 10 via a Freewheeling diode D1, and the emitter of the Darlington transistor Q connects to terminal G of the voltage regulator 10. Moreover, the voltage regulator 10 further includes a cut-off switch Q2, wherein the cut-off switch Q2 connects the base and the emitter of Darlington transistor Q. Furthermore, the control terminal of cut-off switch Q2 connects to terminal A of the voltage regulator 10 via a Zener diode D2.
Please refer to FIG. 1 again. When the starting switch 15 turns on, the battery 13 supplies the battery voltage to the base of Darlington transistor Q via the warning light 14 and the current limit resistor Rb so as to turn on Darlington transistor Q. Moreover, the battery 13 outputs an exciting current to the exciting winding 122 of generator 12 through the conducting Darlington transistor Q. Then the generator 12 starts to build up the output voltage.
The generator 12 transmits the output voltage to cut-off switch Q2 so as to turn on cut-off switch Q2 after the generator 12 has built up the output voltage. Moreover, the cut-off switch Q2 that is turned on couples the base and the emitter of Darlington transistor Q thus cutting off Darlington transistor Q. According to the non-conduction of Darlington transistor Q, the voltage across the exciting winding 122 is gradually reduced through the Freewheeling diode D1. This causes the output voltage generated by the first output terminal T1 of the generator 12 to drop down, which causes the cut-off switch Q2 to be turned off.
Consequently, the Darlington transistor Q turns on again due to the battery voltage generated by the battery 13 while cut-off switch Q2 is turned off. The conduction of Darlington transistor Q excites the exciting winding 122 of generator 12 so that the output voltage of generator 12 is raised up again.
The disadvantage of this arrangement is that the functionality of voltage regulator 10 depends on the power rating of the warning light 14, which must be about 3 W. When warning lights with a power rating of 2 W or 1.4 W or high light LEDs are used, the exciting current flowing through exciting winding 122 will be too low, and consequently the generator 12 will build up the required output voltage only at high speed of rotation.